1. Field of Invention
The present invention relates to a measure technique for a Thin Film Transistor Liquid Crystal Display (TFT-LCD), more particularly, to a method and a device for measuring flicker of liquid crystal modules.
2. Description of the Prior Art
In the usage of liquid crystal panels, polarities switch of common voltage signals (Vcom) causes horizontal strip flickers, known as Flicker phenomena. Flicker value is a direct indicator of quality and reliability of liquid crystal panels. Generally, the lower the flicker value is, the fewer the risk of Image Sticking (IS) on liquid crystal panels is, and vice visa. Therefore, measuring flicker value and keeping flicker value within a preset range is an unavoidable challenge in designing and manufacturing liquid crystal panels.
Conventionally, to measure flicker value, methods such as FMA, JEITA and VESA are usually applied. These conventional methods are common in quantifying an observation of viewing flicker in terms of flicker values. FMA takes ratio of AC component to DC component of luminance variation as flicker values. JIETA and VESA apply Fast Fourier Convertation (FFT) to measure decibel value of every flicker frequency respectively, then integrate over the spectrum or locate the greatest decibel value. These methods can quantitatively analyze the observation of viewing flicker, however these methods does not directly represent Flicker phenomena caused by polarities switch of common voltage signals Vcom. Moreover, the measured flicker values may not correctly reflect a shift of common voltage signals Vcom due to other causes, such as a flicker of a backlight or unstable ground wire, etc.